The disclosure concerns a digital printer for printing to a recording medium with toner particles that are applied with the aid of a liquid developer, in particular a high-speed printer for printing to web-shaped or sheet-shaped recording media.
In such digital printers, a latent charge image of a charge image carrier is inked by means of electrophoresis, with the aid of a liquid developer. The toner image that is created in such a manner is transferred indirectly (via a transfer element) or directly to the recording medium. The liquid developer has toner particles and carrier fluid in a desired ratio. Mineral oil is advantageously used as carrier fluid. In order to provide the toner particles with an electrostatic charge, charge carrier substances are added to the liquid developer. Further additives are additionally added, for example, in order to achieve the desired viscosity or a desired drying behavior of the liquid developer.
Such digital printers have long been known, for example, from DE 10 2010 015 985 A1, DE 10 2008 048 256 A1 or DE 10 2009 060 334 A1.
To ink the charge images on the charge image carrier, liquid developer is directed past the charge image carrier by a developer station. The developer station has in a known manner a developer roller that directs the liquid developer past the charge image carrier; an application system that supplies the liquid developer to the developer roller; and a cleaning unit that cleans off the residual liquid developer remaining on the developer roller after the inking of the charge images on the charge image carrier. The cleaning unit provides, for example, a cleaning roller that removes the residual liquid developer from the developer roller; an electric field thereby exists between developer roller and cleaning roller that promotes the transfer of the residual liquid developer, for example. The residual liquid developer can be scraped off the cleaning roller by a blade. No residual toner should thereby remain on the cleaning roller, since otherwise this could arrive at the developer roller again.
Developer stations in which liquid developer is supplied to a charge image carrier are known. In U.S. Pat. Nos. 7,522,865 B2, 7,292,810 B2, 6,895,200 B2, developer stations are described in which liquid developer is directed past a developer roller. Arranged adjacent to the developer roller is an electrode between which and the developer roller the liquid developer is directed. An electrical voltage via which the toner is attracted to the developer roller exists between the electrode and the developer roller. Before the liquid developer is supplied to the charge image carrier, it travels through a gap (nip) that exists between a dosing unit (a blade or a dosing roller) and the developer roller. The dosing unit is at such an electrical potential that the toner migrates towards the developer roller; the thickness of the liquid developer layer on the developer roller is simultaneously established. Examples of a dosing unit are described in WO 2006/090352 A1 and US 2002/0159794 A1.